1. Field of the Invention
The present invention relates to a light-emitting device used for a backlight for a liquid crystal display or the like, a luminaire for room lighting, or a display in a television or the like.
2. Description of Related Art
In recent years, there have been many reports on organic light-emitting elements using organic materials as light-emitting materials, for example, in Applied Physics Letters, Vol. 51, page 913, 1987. The organic light-emitting elements are characterized by planar light emission, and the ones having a high efficiency of more than 40 lm/W have just begun to be reported recently, for example, in 2000 Spring the Japan Society of Applied Physics annual meeting (31a-H-3). These studies have raised expectations for new luminaires and displays using planar light-emitting bodies.
Conventional light sources include spherical bulbs using a filament and rod-shaped lamps utilizing a discharge phenomenon. Accordingly, when being used as a luminaire, they can be categorized into direct illumination and indirect illumination. In the direct illumination, a reflecting hood for reflecting light emitted upward and sending it downward is provided, while in the indirect illumination, a reflecting plate for diffusing light or reducing glare is provided. On the other hand, electroluminescence panels (EL panels) are characterized by planar light emission. They are expected to develop as a new luminaire and be applied as a light source for display.
The EL panels can be classified mainly into inorganic EL elements and organic EL elements. The organic EL elements have an advantage in that they can be driven at lower voltage than the inorganic EL elements and emit light more efficiently. Furthermore, since they are as efficient as light-emitting diodes (LEDs) and easy to produce, their use as a future light source is expected.
However, the organic EL elements have a problem of short lifetime in a high-luminance application. The reason is that, since their efficiency is lower than fluorescent lamps emitting light at least at a high efficiency of 80 lm/W, the organic EL elements have to be used under heavier load conditions in the high-luminance application.
Thus, there has been a problem that the organic EL elements with the conventional planar structure cannot achieve a sufficiently long lifetime as a light source usable in the high-luminance application.
On the other hand, in order to increase the luminous flux obtained from a light-emitting surface of the organic EL element, a surface area thereof can be increased. An increase in the surface area of the organic EL elements can improve a leading-out efficiency of light. There are various methods for increasing the surface area. For example, a surface of a substrate 71 is formed to be rough as in a light-emitting element 70 shown in FIG. 7, or an anode 72 is patterned to be rough. Subsequently, a light-emitting layer 73 and a cathode 74 further are formed thereon. Alternatively, as shown in FIG. 8, planar or rough light-emitting elements 81, 82 and 83 are laminated so as to form a layered light-emitting element 80.
However, these conventional methods pose a problem in that the surface area of the organic EL elements is, at most, about two to three times as large as the conventional elements and cannot be increased drastically.
It is an object of the present invention to solve the conventional problems described above and to provide a light source with an extended lifetime even in a high luminance application by increasing a surface area of a light-emitting element drastically so as to reduce a current amount per unit area.
In order to achieve the above-mentioned object, a light-emitting device of the present invention includes a plurality of light-emitting elements provided on a base material. Each of the light-emitting elements includes a pair of electrodes, and a light-emitting layer interposed between the electrodes. Light-emitting surfaces of the light-emitting elements are arranged along a standing direction with respect to the base material.
In the light-emitting device of the present invention, the light-emitting elements can be formed into a belt shape.
In the light-emitting device of the present invention, the light-emitting elements can be formed into a strap shape.
Also, in the light-emitting device of the present invention, the light-emitting elements can be formed into a cylindrical shape or a columnar shape.
Furthermore, in the light-emitting device of the present invention, the light-emitting elements can be formed to be porous.
Moreover, the light-emitting device of the present invention can use a layered light-emitting element formed by laminating a plurality of light-emitting elements, each comprising a pair of electrodes and a light-emitting layer interposed between the electrodes.
In the light-emitting device of the present invention, the light-emitting layer of the light-emitting elements may be formed of an organic material.
Alternatively, in the light-emitting device of the present invention, the light-emitting layer of the light-emitting elements may include a plurality of organic materials having different emission colors.
In the light-emitting device of the present invention, the organic material may be dispersed.
Alternatively, in the light-emitting device of the present invention, the organic materials may be isolated according to their emission colors.
In the light-emitting device of the present invention, the light-emitting layer of the light-emitting elements may include a plurality of layers, each being a layer formed of an organic material having an emission color different from each other.
In the light-emitting device of the present invention, a hole transport layer may be laminated on the light-emitting layer of the light-emitting elements.
Furthermore, in the light-emitting device of the present invention, an electron transport layer may be laminated on the light-emitting layer of the light-emitting elements.
In addition, a light-emitting device of the present invention includes a layered light-emitting element formed by laminating 10 to 500 light-emitting elements, each including a pair of electrodes, and a light-emitting layer interposed between the electrodes.